In an automatic tasking machine such as a machine tool or a robot, in the course of its working movements it will apply forces to workpieces and be subject to actions of forces from outside. In this case, the automatic working machine is required to detect forces and moments acting on it from outside and to perform control corresponding to these forces and moments. And to perform control corresponding to forces and moments with high accuracy, it is necessary to detect the forces and moments acting from outside exactly.
In this connection, various force-sensing sensors have been proposed in related art. Generally, force-sensing sensors can be classified by their detection methods into elastic-type force-sensing sensors and balance-type force-sensing sensors. An elastic-type force-sensing sensor measures an external force on the basis of an amount of deformation proportional to the force. A balance-type force-sensing sensor measures a force by balancing it with a known force.
Force-sensing sensors having as their principle structure a structure in which multiple strain resistance devices are provided on a part of a straining body that deforms elastically in correspondence with external forces are known. When an external force acts on the straining body of a force-sensing sensor, electrical signals corresponding to degrees of deformation (stress) of the straining body are outputted from the multiple strain resistance devices. And on the basis of these electrical signals it is possible to detect two or more components of force acting on the straining body. Measurement of the stress arising in the force-sensing sensor is carried out by calculation on the basis of the electrical signals.
One known force-sensing sensor is the six-axis force sensor. A six-axis force sensor is a kind of elastic-type force sensor, and has multiple strain resistance devices on straining body parts. A six-axis force sensor resolves an external force into stress components (forces Fx, Fy, Fz) in the axis directions of the three axes (X axis, Y axis, Z axis) of an orthogonal coordinate system and torque components (moments Mx, My, Mz) of the axis directions, and detects them as six axis components.
A first example of a six-axis force sensor of related art is the ‘Multiple Force Component Load Cell’ disclosed in JP-B-63-61609. The six-axis force sensor disclosed in this publication has a construction in which multiple strain gauges are affixed to a straining body with a three-dimensional structure. With a structure in which strain gauges are affixed to a straining body, there are problems such as that the scope for size reduction is limited; manufacturing reproducibility is poor and dispersion arises among products; and affixing layers detach due to stress of repeated impacts and thermal stresses and the like.
A second example of a six-axis force sensor of related art is the ‘Device for Detecting Two or More Force Components’ disclosed in Japanese Patent Publication No. 2746298. In a six-axis force sensor disclosed in this publication, multiple strain resistance devices are made on a semiconductor substrate using semiconductor manufacturing processes, and strain gauge elements are thereby provided integrally with a straining body part.
The six-axis force sensor of this second related art example structurally has the characteristic that when an attempt is made to detect a force or moment on each of three orthogonal axes, the whole substrate distorts isotropically, and also has the problem that the disposition of the multiple strain resistance devices on the substrate is not optimal and an external force acting on the straining body part cannot be resolved into components with good accuracy. In six-axis force sensors, when for example an external force is applied so that only an axial stress component Fx arises, if outputs are produced by stresses in connection with components other than Fx, which should properly be 0, exact force detection is impossible, and this is problematic.
Generally in a multi-axis force sensor the problem of not being able to resolve the axis components (forces and moments) of an external force acting on the straining body is known as the problem of ‘other axis interference (cross-talk)’. This problem of other axis interference is one which cannot be ignored from the point of view of realizing a practical multi-axis force sensor.
As technology for solving this problem of other axis interference, the present inventors have proposed a six-axis force sensor having a new construction, in JP-A-2003-207405. In this six-axis force sensor, multiple strain resistance devices are integrally provided in a predetermined disposition pattern on parts of a straining body on a semiconductor substrate using semiconductor manufacturing processes.
This six-axis force sensor consists of a platelike semiconductor substrate having an approximately square plan shape, and is made up of a support part at its periphery, an approximately square action part positioned centrally, and connecting parts connecting the four sides of the action part to corresponding parts of the support part.
The strain resistance devices are provided at the boundaries between the sides of the square action part and the connecting parts. With this six-axis force sensor, the problem of ‘other axis interference’ is solved by improving the form of the straining body parts and optimizing the disposition pattern of the multiple strain resistance devices.
In the six-axis force sensor set forth in JP-A-2003-207405, because the strain resistance devices inherently have temperature-dependent characteristics, resistance devices for temperature compensation are provided on the semiconductor substrate. The temperature-compensating resistance devices are used for calculating a resistance ratio between a resistance value at room-temperature and an actual resistance value. By temperature-compensation of the resistance values of the strain resistance devices being carried out on the basis of the calculated resistance ratios and the surrounding temperature, the influence of the surrounding temperature is lowered and more accurate stress detection is made possible.
These temperature-compensating resistance devices are provided on the support part at the periphery of the semiconductor substrate. Because the temperature-compensating resistance devices are provided in positions away from the multiple strain resistance devices, the situation has arisen that thermal influences dependent on the substrate and interconnection parts such as heat conduction levels and thermal expansion levels are different between the areas where the strain resistance devices were disposed and the areas where the temperature-compensating resistance devices were disposed. And, stresses from the metal material and adhesive in the support part have also had an influence. As a result, there has been the problem that it the temperature compensation values of the temperature-compensating resistance devices do not necessarily assume the optimal values for performing output correction of the strain resistance devices.
On the other hand, when to make the temperature conditions the same the temperature-compensating resistance devices are disposed near the strain resistance devices, because the temperature-compensating resistance devices also distort under stress to the action part, and undergo resistance changes, the problem arises that they do not perform their temperature-compensating function.